Nickel-cadmium batteries, nickel-hydrogen batteries, nickel-zinc batteries, and lithium secondary batteries are commercially available secondary batteries. Among them, the lithium secondary batteries have almost no memory effect compared to nickel-based secondary batteries, and are capable of being freely charged and discharged. Also, the lithium secondary batteries have very low self-discharge rates and high energy densities, so that the lithium secondary batteries have attracted much attention.
A lithium secondary battery mainly uses a lithium-based oxide and a carbon material as a positive electrode active material and a negative electrode active material, respectively. The lithium secondary battery includes an electrode assembly in which a positive electrode plate and a negative electrode plate respectively coated with the positive electrode active material and the negative electrode active material are disposed with a separator therebetween, and an external member (i.e., a battery case) configured to hermetically store the electrode assembly along with an electrolyte solution.
In general, lithium secondary batteries may be classified into a can-type secondary battery in which an electrode assembly is embedded in a metal can and a pouch-type secondary battery in which an electrode assembly is embedded in a pouch of an aluminum laminate sheet, depending on a shape of an external member.
Recently, secondary batteries have been widely used not only in small-sized devices, such as portable electronic devices, but also in middle- or large-sized devices, such as automobiles or electric power storage devices. When used in middle- or large-sized devices, a large number of secondary batteries are electrically connected to increase capacity and output. In particular, pouch-type secondary batteries are frequently used for the middle- or large-sized devices because the pouch-type secondary batteries are easy to stack.
However, since a pouch-type secondary battery is generally packed in a battery case of a laminate sheet including aluminum and polymer resin, the pouch-type secondary battery does not have high mechanical rigidity. Accordingly, when a battery module is configured with a plurality of pouch-type secondary batteries, a cartridge is often used to protect the secondary batteries from external impact, prevent motion of the secondary batteries, and facilitate the stacking of the secondary batteries. The term “cartridge” may be replaced by various other terms, such as a cell cover.
One cell cartridge assembly is provided by accommodating approximately two secondary batteries per cartridge, and one battery module may be configured by assembling a plurality of cell cartridge assemblies. Here, the cell cartridge assemblies, each of which is a basic unit of the battery module, occupy the largest quantity among components of the battery module. Accordingly, it takes the most time to prepare the cell cartridge assemblies during a process of producing the battery module.
Meanwhile, the assembly of a conventional cell cartridge assembly may include stacking two secondary batteries on a top surface of a lower cartridge, and then covering the stacked secondary batteries with an upper cartridge. However, in this case, it is not easy to quickly and accurately stack unit secondary battery cells on the lower cartridge every time. Thus, there is a problem that the time required to assemble one cell cartridge assembly increases. Furthermore, an assembly tolerance is highly likely to occur depending on a degree of skill of an operator. The assembly tolerance may be a factor that adversely affects performance of the battery module.